Kotlin Kotlin Collections and Generics 2

Question 1

What does `associateBy` do in Kotlin collections?

Accepted Answer

Creates a Map from a collection using a key selector

Answer

`associateBy` transforms a collection into a `Map<K, T>` using a key selector, with each element as the value.

Question 2

What is the difference between `any` and `all` in Kotlin collections?

Accepted Answer

`any` returns true if at least one element matches; `all` returns true only if every element matches

Answer

`any` returns true if at least one element satisfies the predicate; `all` returns true only if every element satisfies it.

Question 3

What does `partition` do in Kotlin?

Accepted Answer

Splits a collection into two lists: matches and non-matches based on a predicate

Answer

`partition` returns a `Pair, List>` where the first list contains elements matching the predicate and the second contains the rest.

Question 4

What is the purpose of generics in Kotlin?

Accepted Answer

To enable type-safe reusable code that works with different types

Answer

Generics allow writing type-safe classes and functions that work across different types without duplicating code.

Question 5

What does `out T` (covariance) mean in Kotlin generics?

Accepted Answer

T can only be produced (returned), making the generic covariant

Answer

The `out` modifier makes a type parameter covariant — the generic can only produce values of type T, not consume them.

Kotlin Practice Test